1. Field of the Invention
This invention relates to optical storage of information in the form of binary data on a coated medium. More particularly, this invention relates to media adapted to storage of encoded data in the form of an array of spots on an optically reflective medium. The spots are formed by application of a laser beam focussed upon an extremely small point on the medium as the data is being recorded.
2. Description of the Prior Art
Interest in the development of optical data storage systems has been stimulated recently by the introduction of optical video disk systems and the continued improvement in potentially inexpensive GaAlAs laser diodes. One of the major obstacles to the introduction of these systems is the development of suitable optical storage materials. A candidate material should exhibit; 1) low writing energy (compatibility with GaAlAs lasers), 2) long lifetime and 3) low cost. Several material systems have been investigated including (A) Thin Metal Films, D. Mayden, Bell Systems Technical Journal 50, 1761 (1971); and P. Kivits, P. Zalm and R. DeBont, OSA/IEEE Conference on Laser and Electrooptic Systems, San Diego, Calif. (February 1980) (unpublished); (B) Organic Dyes, V. Norotny and L. Alexandra, Journal of Appl. Polymer Science, 24, 1321-1323 (1979); V. B. Jipson and C. R. Jones, SPIE Proceedings, Infrared Dyes for Optical Storage, J. Vac. Sci. Technol., 18 No. 1 105-109 (Jan./Feb. 1981); (C) Dye Loaded Polymers, D. G. Howe and J. J. Wrobel, Solvent-Coated Organic Materials for High Density Optical Recording, J. Vac. Sci. Technol. 18 No. 1 92-99 (Jan./Feb. 1981); (D) Metal Loaded Polymers, J. Drexler, "Drexon Optical Memory Media for Laser Recording and Archival Data Storage" J. Vac. Sci. Technol. 18 No. 1 87-91 (Jan./Feb. 1981), T. W. Smith and A. T. Ward, Materials Research Society Meeting, Boston, Mass., (November 1980) (unpublished); and (E) bilayers, R. C. Miller, R. H. Willens, H. A. Watson, L. A. D'Asaro and M. Feldman, The Bell System Technical Journal, 58, 9, (1979).
U.S. Pat. No. 4,252,890 of Haas et al for "Imaging Systems Which Agglomerates Particle Material" describes in connection with FIG. 6 a method of forming an optical image by using a substrate of polyethylene terephthalate coated with a microscopically discontinuous layer of an amorphous selenium imaging material 0.2 micrometer thick to produce an image by agglomeration or fusing, of the selenium layer into particles in response to illumination of the medium with a source of energy greater than 0.2 joule/cm.sup.2 through a mask. The result was a faithful image of the mask. At an energy level above 0.3 joule/cm.sup.2 the selenium was evaporated in the areas illuminated through the mask. Useful coating materials are selenium, arsenic, silver, cadmium, zinc, tellurium, and radiation absorbing pigments and dyes.
U.S. Pat. No. 4,188,214 of Kido et al entitled "Recording Material" describes a laser recording material involving use of a recording medium of two materials, one of which is metal and the other of which is a compound such as a metal sulfide other than GeS, a metal fluoride or metal oxide. In the Kido patent it is suggested that the metal layer be a single layer formed of a mixture of the metals such as Au, Pt, Rh, Ag, Al, Ti, Cr, W, Cu and Te as well as many others cited in Col. 2 of the Kido patent, which are less relevant to the instant invention. No suggestion of the concept of using a polymeric or organic matrix to support the metal particles was suggested. FIG. 3 shows particles of metal supported in a matrix of the compound. The compounds are employed because of their energy absorbing characteristics to pass heat into the metal particles to increase the sensitivity of the recording material. Also, the compounds have a higher melting point than the metal materials which are more reflective. The compounds are also more stable chemically and not hygroscopic. The method of operation of the recorder is to deform or evaporate the medium.
U.S. Pat. No. 4,069,487 describes coating of an optical storage layer with an organic or inorganic layer for protection. In FIG. 6 of that patent, the optical storage layer is a laminate of a non-metallic layer and a metallic layer which combine to form a recording layer.